Integration, catalyzed by the viral integrase protein, is an essential step in the life cycle of all retroviruses, and the integrase enzyme of human immunodeficiency virus type 1 (HIV-1) is a common target of the highly active antiretroviral therapies that are used to treat AIDS patients. Integrase strand transfer inhibitors (INSTIs) have been in clinical use since 2007, and the prior iteration of this renewal application critically discovered their mechanism of action. The target of the INSTIs is the integrase-viral DNA nucleoprotein complex, also known as the intasome, and the understanding of the mechanism of therapeutic action is greatly facilitated through the study of detailed 3- dimensional structure of drug targets. Although a high-resolution structure of the HIV-1 intasome has yet to be reported, we have reported numerous structures for the prototype foamy virus (PFV) intasome, which is also inhibited by the INSTIs. Using this model, we previously described that INSTIs work by ejecting the critical deoxyadenylate residue of viral DNA and its associated 3'-hydroxyl nucleophile from the integrase active site, disarming the integration machinery. During the current funding period we extended this observation to discover that INSTIs are structural mimics of the chemical attacking and leaving groups of the DNA strand transfer reaction. Herein we provide preliminary data for a new retroviral intasome structure, and we will use this new structural information together with the structure of the PFV intasome to refine our working model of the HIV-1 intasome, the clinically relevant INSTI target. We have discovered that the most intriguing integrase drug class since the INSTIs, the allosteric integrase inhibitors (ALLINIS), inhibits HIV-1 particle maturation, implying a structural role for integrase in HIV-1 particle morphogenesis. The role of integrase in forming the infectious HIV-1 structure will be elucidated using a variety of biochemical and genetic techniques. This line of research will culminate with a biologically realistic model for the HIV-1 intasome to aid novel INSTI development and with an acute vision of the mechanism of ALLINI action, which will inform the clinical development of this new and important anti-HIV drug class.